1. Field of the Invention
The present invention relates to an apparatus and method for synchronized playback of video and audio data, and particularly to a synchronized playback of audio and video data for data having a plurality of audio data.
2. Description of the Related Art
As an international standard for encoding video data and audio data and multiplexing of those data, MPEG (Moving Picture Expert Group) standard is widely known. Information called PTS (Presentation Time Stamp) is included in video/audio data recorded in accordance with the MPEG standard. PTS contains information for synchronizing the time. For example in a stream having a plurality of audio data corresponding to video data, PTS enables to continue playing video while switching only the audio.
Along with an increasing usage of a playback apparatus for video/audio recorded in MPEG format, software that uses a device or a personal computer for recording video/audio in MPEG format are becoming widely used. There are some software that produce MPEG streams without PTS as they understand the MPEG standard in their own ways. With such a MPEG stream without PTS, video and audio must both be stopped before switching the audio so that the video and audio can be synchronized to resume playing the MPEG stream.
A technique for synchronizing in such a MPEG stream is disclosed in Japanese Unexamined Patent Publication No. 6-275053 (Yamamoto). The technique disclosed by Yamamoto assumes that audio data is always inserted at a constant interval. Virtual PTS for audio data is calculated under this assumption using a characteristic of CD, which is a recording medium. Further, video and audio data are synchronized by synchronizing the virtual PTS with PTS associated with the video data. However the present invention has recognized that the technique disclosed by Yamamoto requires to use a characteristic of recording media in order to obtain a virtual PTS for audio data.